There has been a growing interest for generation and radiation of ultra-short impulses in silicon. These impulses can be used in 3D imaging radars, spectroscopy, high-speed wireless communication, and precision time/frequency transfer. Today, in the realm of Terahertz (THz), pulse radiating systems are based on two conventional methods. The first method employs a femtosecond-laser-based photoconductive antenna (PCA) that is usually fabricated on a III-V semiconductor substrate. A femtosecond-laser-based THz time-domain spectroscopy (THz-TDS) system has been built based on the vastly researched terahertz photoconductive antennas (PCA). However, there are several critical limitations with current THz-TDS systems, including the need for a laser, limited average radiated power, and need to move the imaging target mechanically. In the second method, oscillator-based integrated circuits are designed that radiate mm-wave pulses in silicon. Current silicon-based pulse radiating systems are based on on-chip voltage-controlled oscillators (VCO) and/or power amplifiers (PA) as switches such as, work using the phase of the carrier signal synchronized to an external reference with a phase-locked loop (PLL). However, there are several limitations with this method of pulse generation, including bandwidth limitations, RF leakage, power demands, and limited scalability.
Ideally, the impulses should be very short in time and provide a large peak power. Their pulse width limits the depth resolution and their peak power determines the range of the measurement. Impulse generation methods can be divided into two main categories. In the first category, a continuous-wave signal is generated on-chip and a switch is used to modulate the amplitude of the continuous-wave and convert it to short impulses. For example, the shortest radiated impulse reported with this method is 26 psec, which was based on a noisy envelope of the radiated signal.
The second category is based on the technique of direct digital-to-impulse radiation, which was introduced for the first time in M. M. Assefzadeh and A. Babakhani, “A 9-psec differential lens-less digital-to-impulse radiator with a programmable delay line in silicon,” Radio Frequency Integrated Circuits Symposium, 2014 IEEE, vol., no., pp. 307, 310, 1-3 Jun. 2014; and M. M. Assefzadeh and A. Babakhani, “An 8-psec 13 dBm peak EIRP digital-to-impulse radiator with an on-chip slot bow-tie antenna in silicon,” Microwave Symposium (IMS), 2014 IEEE MTT-S International, vol., no., pp. 1, 4, 1-6 Jun. 2014. In this technique, no on-chip oscillator was used. Instead, a fast trigger signal is generated and used to release the DC energy stored in a broadband on-chip antenna. For example, radiation of 9-psec impulses may use an on-chip differential inverted-cone antenna. Further, 8-psec impulses may be radiated using an on-chip slot bow-tie antenna. Such chips may be based on a single element and without on-chip delay control. Furthermore, these impulse radiators may be fabricated using a 130 nm SiGe BiCMOS process. In the prior application PCT/US2014/058019 filed on Sep. 29, 2014, direct digital-to-impulse high-resolution radar imaging systems and methods were disclosed.
The fully-programmable digital-to-impulse radiating array discussed herein provides the ability to control delay at each individual element, near-ideal spatial combing, and beam steering.